The present invention relates generally to a self-detecting type of SPM probe and, more specifically, to the structure of a self-detecting type of SPM probe using a cantilever type of SPM probe with U shaped piezo-resistors provided on a semiconductor substrate.
The SPM (Scanning Probe Microscope) is used to find out the surface shape and change in physical characteristics of minute particles of the order of an atom in size. The SPM device uses an SPM probe with a tip provided at the end of a scanning probe. In the SPM device using the SPM probe described above, by scanning a surface of the sample with the tip provided at the edge of the probe, an interaction (such as an attractive force or repulsive force) is generated between the surface of the sample and the tip, and through detection of the amount of deflection of the SPM probe caused by the interaction, the shape of the surface of the sample is measured.
As for the amount of deflection of the SPM probe, a piezo-resistive probe with piezo-resistors formed on the surface of a semiconductor is provided and fluctuations in resistance are measured to detect the amount of deflection. The SPM probe as described above is referred to as a self-detecting type of SPM probe.
This self-detecting type of SPM probe based on the conventional technology is generally produced, as shown in FIG. 16 and FIG. 17, in a cantilever form. The SPM probe 180 in FIG. 17 comprises a cantilever 182 and a reference 184 for measuring a reference resistance value, and p+ piezo-resistors 188 and 190 are formed on the cantilever 182 and the reference 184 respectively by selectively implanting p-type impurity ions in a U shape (Refer to FIG. 16) into the surface of an n-type silicon substrate 186.
Then, on the surface of the silicon substrate 186 a silicon oxide (SiO2) film 192 is formed for protecting the surface excluding the metal contact sections of the cantilever 182 and the reference 184, and aluminum (Al) electrodes 194, 196, 198 and 200 for contacting are embedded in the metal contact sections respectively. It is assumed herein that p-type impurity ions are implanted into the surface of the n-type silicon substrate 186 to form p+ piezo-resistors 188 and 190, but when a p-type silicon substrate is used, n-type impurity ions are implanted into the surface of the substrate to form n+ piezo-resistors.
In the self-detecting type of SPM probe 180 based on the conventional technology, when the surface of a sample is scanned with the cantilever 182 of the scanning probe microscope with a tip provided at the edge thereof (not shown), an attractive force or a repulsive force according to an inter-atomic force is generated between the surface of the sample and the tip, resistance in the piezo-resistors 188 varies when the cantilever 182 deflects due to the inter-atomic force, and the amount of deflection of the cantilever 182 is detected according to the resistance variations. The variations in the resistance of the piezo-resistors 188 of the cantilever 182 are measured using the aluminum electrodes 194 and 196 of the metal contact sections.
Measurement of resistance values is made in the reference 184 concurrently with the operation described above. This measurement is made to provide reference resistance values for executing temperature compensation by using a Wheatstone bridge because a resistance value in a piezo-resistor itself varies according to ambient and other conditions (such as a temperature condition) rather than deflection caused by the sample.
Self-detecting type of SPM probe using a piezo-resistor is described in, for instance, Japanese Patent Laid-Open Publication No. HEI 5-196458, U.S. Pat. Nos. 5,444,244, and 5,345,815.
However, in the self-detecting type of SPM probe based on the conventional technology, the piezo-resistors 188, 190 of the cantilever 182 and the reference 184 are located in a U shape on the surface of the semiconductor substrate 186 so that current leakage occurs between the legs of the piezo-resistor opposite to each other with the semiconductor substrate 186 therebetween (e.g. between the legs of the resistors 188, between the legs of the resistors 190, and between the resistors 188 and 190), and variations in resistance in piezo-resistors can not be detected accurately.
In addition, when light is irradiated around the piezo-resistors 188, 190, carriers are generated on the surface of the semiconductor substrate 186, and noise occurs when resistance is measured, so that variations in the resistance in piezo-resistors can not be detected accurately.
The problem of light can be eliminated by covering each of the piezo-resistors with a light shielding material, but there is the problem that the object to be covered is extremely small and it is required that the cantilever 182 is deflectable along a shape of the surface of a sample, and for these reasons it is difficult to cover a piezo-resistor with a light-shielding material.
It is an object of the present invention to provide, for solving the problems described above, a self-detecting type of SPM probe which can prevent a current from leaking between adjacent legs of U-shaped piezo-resistors or between adjacent piezo-resistors through a semiconductor substrate and which can prevent noise from being generated due to the influence of carriers generated in response to irradiation of light over the resistors, and which can accurately detect the amount of deflection of a cantilever.
In accordance with one aspect of the present invention, an insulation processing is carried out on the semiconductor substrate between adjacent legs of U-shaped piezo-resistors to separate the elements from each other electrically, so that occurrence of a leak current or noise generated by carriers generated due to incident light can be prevented, which allows accurate detection of the amount of deflection of the cantilever.
In accordance with another aspect of the present invention, a reference with piezo-resistors is formed adjacent to a cantilever and insulation processing is also carried out on the semiconductor substrate between adjacent legs of the U-shaped piezo-resistor of the reference to separate the elements from each other electrically, so that occurrence of a leak current in a reference or noise generated by carriers produced due to incident light can be prevented, which allows an accurate detection of the amount of deflection of a cantilever.
In accordance with another aspect of the present invention, as the insulation processing, impurity diffusion layers each consisting of a conductive type reverse to that of the semiconductor substrate are formed in the space in the semiconductor substrate at least on the side that face each other of piezo-resistors located opposite to each other with the semiconductor substrate therebetween, and the elements are separated from one another electrically, so that occurrence of a leak current or noise generated by a carrier due to light can be prevented.
With the present invention, as the insulation processing, piezo-resistors are formed on semiconductor layers each formed in the same U shape as that of the resistor and an insulated layer is provided between the semiconductor layer and the semiconductor substrate to separate the elements from one another electrically, so that occurrence of a leak current or noise generated by a carrier due to light can be prevented.
With the present invention, as the insulation processing, impurity diffusion layers each consisting of a conductive type reverse to that of a semiconductor substrate are formed in each space in the semiconductor substrate at least on the sides that face each other of piezo-resistors located to each other with the semiconductor substrate therebetween, and insulators are also formed in the semiconductor substrate between the piezo-resistors opposite to each other to separate the elements from one another electrically, so that occurrence of a leak current or noise generated by a carrier due to light can be prevented.
With the present invention, above described probe with less leakage of light is used in the SPM device, so that, a light shielding mechanism that is conventionally required can be eliminated and noise due to leak current can be prevented, and high-efficiency measurement can be made.
Other objects and features of this invention will become clear from the following description with reference to the accompanying drawings.